It is very common to laminate two or more tissue plies in order to produce the final tissue product. Herewith a more flexible and softer tissue product is obtained as compared to if one single ply with a corresponding thickness and basis weight had been produced as for the laminated product. The absorbent capacity and the bulk are moreover improved.
The lamination of two or more tissue plies is often made by means of gluing. A mechanical embossing of the plies is also often performed before they are glued together. It is further known to laminate two plies only by means of a mechanical embossing, at which a mechanical joining of the plies occurs in the embossing sites.
Through for example EP-A-796 727 it is known to first emboss two paper plies in a three dimensional structure with alternating raised and recessed portions, after which glue is applied to one of the plies and the two plies are joined in a press nip between two embossing rolls, so that the raised portions of the respective plies are glued to each other. A similar embossing procedure is shown in EP-A-738 588, according to which the glue also has a colouring effect.
In WO 95/08671 there is disclosed an example of so called nested embossing, in which the two individually embossed plies are combined and joined with the raised portions of one ply nesting into the recessed portions of the opposite ply.
Through U.S. Pat. No. 5,443,889 there is known a procedure for laminating two paper plies, which are fed over a pattern roll each, said pattern rolls having alternating raised and recessed portions and where glue is applied to one ply while this is led over the roll. The two paper plies are then glued together in a nip between the two pattern rolls, which are in register with each other so that a joining and compression of the paper plies occurs in a pattern corresponding to the raised portions of the pattern rolls.
A drawback that occurs in connection with embossing a paper web where this is compressed in spots, is that a considerable strength reduction occurs in the embossing sites, which affects the strength properties of the entire paper product. Strength reductions of up to 70% of an embossed paper as compared to a corresponding unembossed paper are not unusual.
In Swedish patent application no. 0200590-8 there is disclosed a method for producing a multi-ply paper or nonwoven material, by means of gluing the plies wherein a glue transfer roll and a lamination roll are driven in register. The glue transfer roll and the lamination roll have corresponding patterns of protuberances so that the plies are glued together in a pattern corresponding to the configuration of the protuberances.
Printing of tissue paper is often made for aesthetical reasons. The printing pattern could be any pattern including more or less continuous lines, line segments, dots, trademarks, logotypes, symbols, fantasy characters etc. In a multi-ply web material printing is usually made on the outside of the multi-ply web, but may also be on the inner side of one ply, wherein it is visible through the ply.